1. Field of the Invention
The present invention relates to an optical switch which switches the transmission path of an optical signal on the optical fiber in an optical communication system.
2. Description of the Related Art
The optical communication system is used as a trunk-line network system among the current digital network systems. With the recent developments of the optical communication system, the improvement of the propagation loss of the optical fibers, the improvement in the transmission speed of the laser diodes which transform an electrical signal into an optical signal, and the utilization and performance improvement of the erbium-doped fiber amplifier as a type of optical-fiber amplifier.
Moreover, because the multi-media communications are widely spread, the need for the increase in data-transmission capacity and the rapid spread of the Internet, the wavelength-multiplexing optical-communication system which carries out wavelength multiplexing of two or more optical signals with different wavelengths from different information sources and transmits the multiplexed signal on a single optical fiber is used widely, and the degree of the multiplexing is steadily increasing for higher density.
In order to keep the influence of the cut-off failure of the optical fibers between the communication nodes to the minimum or to recover the communication promptly from the failure of the optical fiber, in the optical communication system which carries out the wavelength multiplexing with high density and transmits the high-capacity information signal on the optical fibers, the route changing function is usually assigned to each communication node.
At each communication node, the role of the wavelength add-drop multiplexer to carry out the functions of assigning an input wavelength and multiplexing this signal to be routed over the network is becoming important.
In order to carry out the above-mentioned functions, a 1xc3x972 optical switch which couples one input optical signal with one of two output optical fibers, and a 2xc3x972 optical switch which couples two input optical signals with two output optical fibers respectively, or couples one input optical signal with one of the two output optical fibers are provided.
Especially, in a high-density wavelength-multiplex optical communication system, the number of the optical switches that must be provided in the system is increasing in proportion to the wavelength multiplexing number that is demanded for the optical communication network. Accordingly, there is the demand for a small-size, high-performance optical switch which is suited for high-density assembly on the high-density wavelength-multiplex optical communication system.
FIG. 9A and FIG. 9B show how the optical switch is used in the add-drop equipment.
In FIG. 9A and FIG. 9B, reference numeral 101 is the optical demultiplexer which demuliplexes the wavelength-multiplexed optical signal into the optical signals of individual wavelengths. Reference numeral 102 is a 2xc3x972 optical switch which is coupled to the optical demultiplexer 101, reference numeral 103 is an optical attenuator which can adjust attenuation of the output of the 2xc3x972 optical switch 102, and reference numeral 104 is the optical multiplexer which carries out the wavelength multiplexing of the optical signals of the individual wavelengths from the individual switches.
In the example of FIG. 9A, the through connection is performed for the optical signal of a specific wavelength in the add-drop equipment. For example, in the through connection, the optical signal inputted to the input terminal #1 of the optical switch 102 is outputted to the output terminal #3 of the optical switch 102.
In the example of FIG. 9B, the add-drop connection is performed in order to incorporate the information of the optical signal of a specific wavelength and to send out the information which is different from the incorporated one using the optical signal of the same wavelength. For example, in this add-drop connection, the optical signal inputted to the input terminal #1 of the optical switch 102 is outputted to the output terminal #4 of the optical switch 102, while the optical signal inputted to the input terminal #2 of the optical switch 102 is outputted to the output terminal #3 of the optical switch 102.
That is, in order to realize the add-drop function, the 2xc3x972 optical switch is needed. Although only one 2xc3x972 optical switch which carries out the add-drop function for the optical signal of a single wavelength is shown in FIG. 9A and FIG. 9B, a number of 2xc3x972 optical switches, which is equal to the wavelength multiplex number are required. Therefore, the high-density assembly characteristics are needed for the optical switches.
FIG. 10A and FIG. 10B show an optical switching circuit using a movable prism.
In FIG. 10A and FIG. 10B, reference numeral 105 is the movable prism, and reference numerals 106 and 107 are the two collimated light beams.
In the case of FIG. 10A, the prism 105 does not go into the paths of the collimated light beams as indicated by the dotted line. In this case, the collimated light beams 106 and 107 are not refracted, and they go straight through the optical switching circuit.
In the case of FIG. 10B, the prism 105 is moved to go into the paths of the collimated light beams. In this case, on the incoming plane and the outgoing plane of the prism 105, each of the collimated light beams 106 and 107 is refracted twice. Consequently, the collimated light beams 106 and 107 cross each other in the middle of the prism 105, and they are outputted from the prism 105.
FIG. 11A and FIG. 11B show a changeover switch using an optical waveguide.
In FIG. 11A and FIG. 11B, reference numeral 108 is the first core of the optical waveguide, reference numeral 109 is the second core of the optical waveguide, and reference numeral 110 is the electrode which is used to apply a predetermined voltage to the first core 108.
The first and second cores 108 and 109 are used to form the following optical circuit. That is, at the portions A and C, the distance between the cores 108 and 109 is narrowed so that the directional couplers are formed there which interact the electric fields of the optical signals which are delivered on the both cores. The directional coupler at the portion A is designed such that the optical signal incident to the first core 108 is divided into two equal optical signals at the outputs of the directional coupler and the two equal optical signals are delivered on the first and second cores 108 and 109.
Moreover, the directional coupler at the portion C is designed such that when the optical signals having the same phase from the first and second cores 108 and 109 are incident to the inputs of the directional coupler, both the optical signals are outputted to the side of the first core 108 as shown in FIG. 11A, and when the optical signals having the phase difference xcfx80 from the first and second cores 108 and 109 are incident to the inputs of the directional coupler, both the optical signals are outputted to the side of the second core 109 as shown in FIG. 11B.
On the other hand, in the portion of B, the distance between the cores 108 and 109 is enlarged so as not to interact each other and the electrode 110 is provided to apply a predetermined voltage to the first core 108 only. The known Mach-Zehnder interferometer is thus formed.
In the Mach-Zehnder interferometer, the index of refraction for the optical signal which is delivered on the first core 108 is varied with the voltage applied to the electrode 110, and the phase difference is created over the optical signals having the same phase which are inputted to the first and second cores 108 and 109. In the present case, it is assumed that the phase difference is set to 0 when the voltage is not applied to the electrode 110, and the phase difference is set to xcfx80 when the voltage is applied to the electrode 110.
When the voltage is not applied to the electrode 110, the optical signal inputted to the first core 108 is outputted from the side of the first core 108 as shown in FIG. 11A. On the other hand, when the voltage is applied to the electrode 110, the optical signal inputted to the first core 108 is outputted from the side of the second core 109 as shown in FIG. 11B. Therefore, the changeover switch function can be realized.
In the above-mentioned example, the Mach-Zehnder interferometer is used and the electro-optical effect thereof is utilized to create the phase difference by using the applied voltage. Alternatively, the Mach-Zehnder interferometer may be used in which the thermo-optical effect is utilized to create the phase difference by using the heat source film on one of the first and second cores and controlling the temperature of the heat source film.
Accordingly, by using the optical switch shown in FIG. 10 A-FIG. 11B, the through connection and the add-drop connection are carried out.
In the above example, although the actual structure of the optical switch is not shown in FIG. 10A through FIG. 11B, if the input port is arranged on one side of the optical switch, the output port has to be arranged on the other side of the optical switch as is apparent from FIG. 10A through FIG. 11B.
However, in the conventional optical-communication equipment, such as the add-drop equipment, the input port and the output port are configured in many cases on the same side of the equipment. Taking into consideration the configuration of the conventional optical communication equipment, the adaptation of the optical switch of the type shown in FIG. 10A through FIG. 11B must be considered. In order to arrange the input port and the output port on the same side of the equipment, it is necessary that the bending of the optical fibers on the both sides of the optical switch be performed through the forming process.
When the optical fibers are bent through the forming process, it is impossible to make the radius of curvature of the bending to a radius below a predetermined value due to the physical properties of the optical fibers.
If the optical fibers on the both sides of the optical switch are bent through the forming process in order to arrange the input port and the output port on the same side of the equipment, the problem will arise in that the mounting space and the space required for the forming process become excessively large.
As for the wavelength-multiplex optical communication system the wavelength multiplex number of which is steadily increasing, it is necessary to take into consideration the above-mentioned problem.
An object of the present invention is to provide an improved optical switch in which the above-described problems are eliminated.
Another object of the present invention is to provide an optical switch that can be configured to arrange both the input and output optical fibers on a single side of the optical switch in order to enable high-density assembly.
The above-mentioned objects of the present invention are achieved by an optical switch comprising: a plurality of optical fibers, including input fibers and output fibers, arrayed at equal intervals and in parallel, each of the plurality of optical fibers having a central axis and having an end surface on one side of the optical switch; a single lens having a focal length and a central axis, the central axis of the lens being parallel to the central axis of each optical fiber, the lens disposed away from the end surface of each optical fiber at a distance corresponding to the focal length of the lens; a first mirror having a first reflection surface perpendicular to the central axis of the lens, the first mirror removably disposed at a first position on the other side of the optical switch; and a second mirror having a second reflection surface inclined from the central axis of the lens, the second mirror removably disposed at the first position, wherein the first and second mirrors are configured such that one of the first and second mirrors is selectively disposed at the first position.
The above-mentioned objects of the present invention are achieved by an optical switch comprising: a plurality of optical fibers, including input fibers and output fibers, arrayed in parallel, each of the plurality of optical fibers having a central axis and having an end surface on one side of the optical switch; a plurality of lenses, each having a focal length and a central axis, respectively provided for the plurality of optical fibers, the central axis of each lens being arranged in parallel to and shifted by a predetermined distance from the central axis of each optical fiber, each lens disposed away from the end surface of a corresponding one of the plurality of optical fibers at a distance corresponding to the focal length of the lens; and a plurality of mirrors each having a reflection surface perpendicular to a central axis between one of the input fibers and one of the output fibers, each of the plurality of mirrors, excluding a mirror located on a far-end side of the optical switch in a propagation direction of light, being removably disposed at a crossing-point position corresponding to a position where an optical axis of a light beam from one of the input fibers and an optical axis of a light beam to one of the output fibers cross each other, wherein the plurality of mirrors are configured such that one of the plurality of mirrors is selectively disposed at the crossing-point position.
According to the first aspect of the present invention, when the first mirror is disposed at the position corresponding to the crossing point of the central axis of the lens and the optical axis of the light beam derived by the lens, the optical switch of the present invention serves to couple the light beams sent from the input fibers among the plurality of optical fibers, with the output fibers that are symmetrical to the input fibers with respect to the central axis of the lens. When the second mirror with the inclined reflection surface is disposed at the same position, the optical switch of the present invention serves to couple one of the light beams sent from one of the input fibers with one of the output fibers that is unsymmetrical to that input fiber with respect to the central axis of the lens. Moreover, all the plurality of optical fibers including the input and output fibers are arranged on a single side of the optical switch, and it is possible to provide a small-size optical communication equipment by using the optical switch of the present invention.
According to the second aspect of the present invention, when the first mirror is disposed at the first position corresponding to the crossing point of the optical axis of the outgoing light beam and the optical axis of the incoming light beam, the optical switch of the present invention serves to couple the light beams sent from the input fibers among the plurality of optical fibers, with the output fibers that are symmetrical to the input fibers with respect to the central axis of the lens. When the second mirror is disposed at the second position corresponding to the crossing point of the central axis of the lens array and the optical axis of the incoming light beam, the optical switch of the present invention serves to couple one of the light beams sent from one of the input fibers with one of the output fibers that is unsymmetrical to that input fiber with respect to the central axis of the lens. Moreover, all the plurality of optical fibers are arranged on the single side of the optical switch, and it is possible to provide a small-size optical communication equipment by using the optical switch of the present invention.